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Investments - Additional Information (Details) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2018 USD ($) security | Jun. 30, 2019 USD ($) security | Dec. 31, 2018 USD ($) security
Investment Holdings [Line Items] |  |  |
Available-for-sale investments, cost |  | $ 331,519 | $ 182,325
Par value of mortgage-backed securities pledged to FRB |  | 233,000 | 147,000
Mortgage-backed securities |  |  |
Investment Holdings [Line Items] |  |  |
Available-for-sale investments, cost |  | $ 233,210 | $ 159,937
Number of mortgage backed securities sold | security | 9 |  |
Proceeds from sale of securities | $ 41,000 |  |
Recognized loss from sale of securities | $ 2,000 |  |
Number or mortgage-backed securities with unrealized losses | security |  | 47 | 74
Number of mortgage-backed securities | security |  | 101 | 86
Utah Housing Corporation bonds |  |  |
Investment Holdings [Line Items] |  |  |
Available-for-sale investments, cost |  | $ 21,136 | $ 22,388
Number of securities in net loss position | security |  | 1 |
Ginnie Mae | Mortgage-backed securities |  |  |
Investment Holdings [Line Items] |  |  |
Available-for-sale investments, cost |  | $ 62,000 |
Number or mortgage-backed securities with unrealized losses | security |  | 19 | 34
Fannie Mae | Mortgage-backed securities |  |  |
Investment Holdings [Line Items] |  |  |
Available-for-sale investments, cost |  | $ 110,000 |
Freddie Mac | Mortgage-backed securities |  |  |
Investment Holdings [Line Items] |  |  |
Available-for-sale investments, cost |  | $ 60,000 |

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